Photomasks are used in semiconductor manufacturing processes to transfer patterns onto semiconductor wafers and other substrates. In conventional semiconductor manufacturing processes an integrated circuit design is submitted to a photomask manufacturer in electronic form. The photomask manufacturer converts the integrated circuit design into a photomask pattern that is stored in a pattern data file. This photomask pattern is then transferred to an opaque layer of a photomask to form a photomask that includes a non-opaque substrate and a patterned opaque layer.
One type of photomask, typically referred to as a reticle, is designed for use in a stepper or scanner. The stepper or scanner generates coherent light that passes through the reticle so as to transfer the pattern on the reticle to a photosensitive layer on the semiconductor wafer or other substrate. Reticles are typically formed using a photomask blank that includes a glass plate that is coated with a thin layer of metal, and a photoresist layer that extends over the metal layer. The photomask blank is optically exposed using the photomask pattern. The photomask blank is then developed and etched to pattern the metal layer, forming a reticle having the desired pattern.
Photomask patterns typically include multiple die regions that include structures of varying size and shape. Charge imbalances between the structures on the photomask can lead to electrostatic discharge related defects. More particularly, electrical charge can move between adjacent structures, resulting in damage to the glass plate and/or damage to the patterned metal layer. This damage to the photomask can alter the optical characteristics of the photomask such that the photomask no longer generates the desired optical pattern.
Accordingly, there is a need for a method for forming a photomask having reduced electrostatic discharge related defects. Also, there is a need for a photomask having reduced electrostatic discharge related defects. The present invention meets the above needs.